A base collection is a form of long-term storage. The initial population is used as a bench mark for monitoring changes in genetic diversity over time and after several cycles of regeneration due to genetic drift. It should ensure that seed viability and seed availability of the accessions in the genebank remain at acceptable levels for at least 50 years, which would be one regeneration cycle of a maize genebank accession. It is also used as a back up when the active collection samples are no longer available.

When it should be used

Seeds going into foil bags at CIMMYT (photo: CIMMYT)

The function and operation of the base collection should be supported in the long term through core funding of the institution or government.

The base collection serves the following purposes:

As a duplicate and safety collection of the active collection for long-term conservation.

To reduce the number of regeneration cycles for conservation of the genetic integrity of accessions.

To provide the foundation seed for regeneration of the accessions.

As a black-box seed storage for safety deposits of the cooperative genebanks.

Sample specifications

To conserve as many accessions as possible in a cost effective manner.

Minimum sample size for storage

Normal genebank sample size of maize is 1.5-2 kg (2500-3500 seeds).

Minimum sample size could be 500 g or several regeneration sets (one set is 256-512 seeds).

Minimum viability for storage

The initial viability of the accessions should be more than 95% and it should certainly not be less than 85%. .

Moisture content

Important to maintain seed viability for long term conservation.

The seed moisture content should be balanced at 6-8% in cool drying rooms before packaging the seed samples..

Container specifications

Seed packaging method

To pack the seeds in impermeable pouches and to reduce seed metabolism to a minimum.

Aluminum foil side-gusseted stand-up pouches (one or two pouches) should be filled with the dried seed samples and sealed by a pressured sealer with heat.

An active collection is a medium-term storage. Its purpose is to conserve a large quantity of seeds per accession in order to meet seed requests, as well as to be used for research and enhancement by the genebank. The active collection preserves the germplasm accessions for at least 20 years or for a half of one regeneration cycle in the base collection, as the cost of the regeneration of maize accessions is expensive. (Click for more information on the costs of regeneration from CIMMYT)

When it should be used

The active collection serves to:

Conserve the accessions actively used or expected to be used such as elite lines and populations, core subsets and reference seeds sets of all accessions for management of the genebank.

Distribute seed samples to the users.

Store new introductions and the regenerated seeds before inventorying them.

Store ear and seed samples of the representative germplasm diversity for research and enhancement.

Airtight, thick plastic transparent containers protect the seeds from absorbing moisture and can hold sufficient amounts of seed. They are also handy to access and retrieve seed samples. Containers should have bar code labels inside and outside the container for efficient record-keeping.

Seed packaging method

An airtight, thick plastic container or canister with a lid that can open and close easily.

Steel cans should not be used, as they become rusty with the moisture that forms outside the cans when they are removed from the cold storage.

Glass jars with an airtight lid can also be used.

Specifications of packaging material

Airtight canisters of 3.8 litres (about 2-3 kg of maize seeds). The container should be large enough to hold 2-3 kg (3.9 litres) of seeds.

FAO/IPGRI. 1994. Genebank standards. Food and Agriculture Organization of the United Nations, Rome and International Plant Genetic Resources Institute, Rome. Available in English, Spanish, French and Arabic.